This thesis studies the relationship between three risk factors for criminality: substance use, low IQ and psychopathic traits in male adolescent delinquents of two Dutch juvenile justice centres. New insights in these relationships can bring information to improve treatments and reduce recidivism. There were 1230 participants between 12-25 years old, who were assessed with modules of the Diagnostic Interview Schedule for Children Version IV (DISC-IV; substance use), Wechsler Intelligence Scale for Children-III (WISC-III; IQ)/Wechsler Adult Intelligence Scale-III (WAIS-III; IQ) and Youth Psychopathic traits Inventory (YPI; psychopathic traits). The results of the current study found no difference between the group with and without substance use on full scale (p = .332), verbal (p = .442) and performance IQ (p = .320), but did find a difference between the group with and without substance use on psychopathic traits (p < .001). Male adolescent delinquents who scored positive on substance use showed more psychopathic traits than male adolescent delinquents who scored negative on substance use. There was no significant correlation between IQ and psychopathic traits in the group who scored positive on substance use (r = 0.068, p = .727). There was an unexpected weak positive correlation between IQ and psychopathic traits in the group who scored negative on substance use (r = 0.271, p = .007) in which higher IQ was correlated to more psychopathic traits. There was no difference found in strength of correlation of IQ and psychopathic traits between the group with substance use and in the group without substance use (p = .342). It can be concluded that the relationship between the risk factors IQ, psychopathic traits and substance use in male adolescent delinquents in a juvenile detention centre is not entirely clear. Further research is needed to study the relationship between the risk factors for criminality: substance use, IQ and psychopathic traits.